I. Field of the Invention
This invention relates to tunnel or shaft boring sectional drill pipes comprising a plurality of pipe sections joined together by threaded pin and box type tool joints. The subject invention more particularly relates to the wrenching recesses or "flats" on the drill pipe, which are gripped by a mechanical or manual auxiliary apparatus for "makeup" and "breakout" of the drill pipes.
II. Description of the Prior Art
U.S. Pat. No. 3,768,579 issued to Klein discloses a drill pipe breakout mechanism for a drill pipe that is substantially square in lateral cross-section, having four faces. Each of these four faces has a pair of axially spaced recesses thereon. However, this four-sided drill pipe configuration is inefficient in terms of load sharing because, of the four sides, only two of the sides at a time take substantial loads during makeup or breakout. Thus, for higher torque applications, damage to the wrench recesses or flats is more likely because only two groups of these flats, not all four groups, are sharing the applied torque load.
U.S. Pat. No. 3,802,057 issued to Porter discloses an improvement over the four-sided drill pipe configuration. Namely, the drill pipe in Porter has a portion that is substantially triangular in lateral cross-section and has three faces. A pair of wrench recesses are located on each of the three faces, each pair of wrench recesses being axially spaced. As best seen in FIGS. 12 and 13 of Porter, the two axially spaced recesses comprising each flat set in Porter have different configurations. More specifically, as seen in FIG. 12, the top recess has what is known in the art as a "bathtub" configuration. This configuration is defined as having two adjoining planes which form an angle of greater than 180 degrees (i.e., a reflex angle) as measured from the exterior surfaces of the two adjoining planes. The Porter bathtub configuration has major disadvantages. The bathtub configuration was first implemented to facilitate wrenching in the drive head with an automatic or remote control wrenching arrangement. The bathtub recesses are substantially elongated, such that tangential jaws of the automatic wrenching device can mate therein and allow the drive box to float over the fixed tangential jaws in the drive head. The above configuration leads to a substantially elongated arrangement which protrudes markedly above the work table. This high protrusion is undesirable for machines that are required to be of low profile for underground operation. Furthermore, this bathtub configuration produces an inherent weakness in the drill pipe where the pipe cracks between the pin shoulder of the connection and the innermost machine surface of the bathtub, which is, of course, greatly detrimental to the strength and life of the drill pipe.
FIG. 13 of Porter shows the bottom flat, which is not a recess at all, but is merely a planar portion present on each of the three sides of the triangular drill pipe. The traditional three-sided flat configuration of FIG. 13 is undesirable in that the radial forces associated with this configuration are very high, thus resulting in a very large minimum wrench load being necessary to facilitate makeup and breakout. The higher the minimum wrench load, the more likely that the flats of the drill pipe will be damaged during makeup or breakout.
A need thus exists for a drill pipe having wrenching recesses wherein the wrenching recesses evenly share the applied load.
A need also exists for a drill pipe having wrenching recesses wherein low radial loads are required to facilitate makeup and breakout.
A need further exists for a drill pipe having wrenching recesses which are easy to machine.
An additional need exists for a drill pipe having wrenching. recesses which do not induce cracking of the drill pipe.
Finally, a need exists for a drill pipe having wrenching recesses wherein the portion of the drill pipe having the wrenching recesses and the machine employed to makeup and breakout the drill pipe both have a low profile for use in underground environments.